System and apparatus for electronic control of an absorption refrigeration system

ABSTRACT

This invention relates to a system and apparatus for electronic control of an absorption refrigeration machine. The flow of liquids within the machine, as well as the concentration of the refrigerant/absorbent mixture solution are precisely controlled through the use of solenoid valves. These solenoids are controlled via a microprocessor control system with various sensors attached, which may include fluid level sensors, pressure sensors, temperature sensors and other environmental data sensors.

BACKGROUND OF THE INVENTION

This invention relates to a system and apparatus for electronic control of an absorption refrigeration machine. An ammonia/water type absorption machine is the preferred embodiment, and the example used to disclose the invention, but other combinations of refrigerant/absorbent (for example water and lithium/bromide) may just as easily be used to implement the present invention. The flow of liquids within the machine, as well as the concentration of the refrigerant to absorbent (e.g. ammonia/water solution) are precisely controlled through the use of solenoid valves. These solenoids are controlled via a microprocessor control system with fluid level sensors, pressure sensors, temperature sensors and other environmental data sensors attached.

Conventional absorption refrigeration machines use a refrigerant/absorbent mixture of a fixed concentration. In an ammonia/water absorption cycle, the concentration of ammonia in the mixture determines the temperature of the cooling that occurs, with lower concentrations of ammonia resulting in lower cooling temperatures. Absorption chillers have lower efficiency at colder evaporator temperatures, so energy savings can be achieved by matching the evaporator temperature closely to the target cooling temperature for the cooled space. Furthermore it is common for applications to require different cooling temperatures at different times. It is also desirable to be able to change the ammonia/water concentration to allow the machine to operate at varying ambient outside temperatures. Therefore it is desirable to have an absorption refrigeration system that can cool at varying temperatures, with such cooling temperature being electronically variable.

With reference to block diagram in FIG. 1, a regular ammonia absorption refrigeration machine 100 consists of a Generator 110, a condenser 120, an evaporator 140 and an absorber 160. The generator and condenser operate under higher pressures while the Evaporator and Absorber are at lower pressures. Flow control devices 130, 150 and 180 are required to control the flow between the components. Device 130 controls flow of liquid ammonia from the condenser to the evaporator, where cooling takes place. Device 150 controls flow of ammonia gas into the Absorber 160, where it is absorbed into the ammonia/water solution. Device 180 controls flow of weak ammonia/water solution into the Absorber 160. These flow control devices can be capillary tubes, membranes, needles or other such flow restriction devices. The problems with these devices are that they are prone to mechanical failure or blockage, which may result in failure of the machine. Intricate filtering mechanisms may be required to prevent such failures and these contribute to maintenance costs. Capillary tubes may be too large to be practical in a large machine, due to the high pressures involved a huge diameter is required, and hence a long length of tube is required. Also the risk of ammonia leaks increase in the case of using such a long tube. Another problem with all these fluid flow devices is that they are of fixed operation, and cannot be adjusted according to varying operating conditions, and they are not precise. Present methods of fluid flow control in ammonia absorption refrigeration machines does not allow for precise dosing of fluids to the various components according to real time needs of the machine. Absorption refrigeration machines are exquisitely sensitive to the ambient temperature conditions, and their performance curves change greatly with ambient temperature. This is because the back cooling process, whereby waste heat is removed from the absorber, is sensitive to the ambient temperature. The ability to fine tune and adjust the precise quantities of solution delivered to the various components of an absorption refrigeration machine allows the machine to operate at a higher efficiency across various temperature conditions. The present invention seeks to ameliorate the above shortcomings of existing absorption refrigeration machines by providing a means of providing accurate, reliable and low maintenance fluid control methods and also a means of electronically adjusting the refrigerant/absorbent solution concentration.

DISCLOSURE OF THE INVENTION

The normal ammonia absorption refrigeration machine illustrated in the block diagram of FIG. 1 requires an ammonia pump which pumps strong solution from the Absorber (160) to the, Generator (110). Ammonia pumps are expensive and prone to mechanical failure. Furthermore they do not scale well to small sizes, and consequently this is a limiting factor on producing inexpensive, smaller capacity ammonia absorption refrigeration machines. The machine developed by the present inventors, disclosed herein, does not require any ammonia pump, such pump being replaced with a series of chambers and solenoid valves.

The invention illustrated in FIG. 2 is an example embodiment of an ammonia absorption refrigeration machine that uses pulse width modulated solenoid valves instead of traditional throttle/fluid control devices to control flow between the Generator and the Absorber, and between the Condenser and the Evaporator. Furthermore, it does not require a discrete ammonia pump. It also has an optional feature allowing for the concentration of the ammonia solution to be altered dynamically via electronic control. System 200 comprises a Generator (220) with fluid level (225) and fluid level sensor (230). Heat is applied to the Generator (220), resulting in Ammonia gas flowing to the Condenser (235), which has a fluid level (240) and a fluid level sensor (245). Fluid level sensors may use any suitable electronic fluid level sensing technology. A preferred embodiment uses an optical sensor, which detects a change in total internal reflection of a prism like surface due to the presence of a liquid at the optical interface. Other means may be used to detect fluid levels as well known to anyone skilled in the art.

System 200 uses a series of chambers to move the strong ammonia solution from the region of low pressure to the region of high pressure. The chambers hold the strong ammonia/water solution prior to the solution entering the Generator, hence they are referred to as “Pre-Chambers”. The absorber (265) may typically operate in a pressure range of around 3 Bars, whereas the Generator (220) may typically operate in a range of around 10 Bars. Instead of an ammonia pump, as is usually the case, the invention uses a cyclical batch process whereby strong solution initially enters the first Pre-Chamber, Pre-chamber 1 (280), where it is warmed slightly. This is to prevent the ammonia rapidly boiling out before it reaches the generator (220). The second Pre-chamber, Pre-chamber 2 (205) in FIG. 2, is usually at a higher pressure, but when the solution level (210) is lower than a level determined by a liquid level sensor (215), an electronic solenoid valve (284) is opened. This results in the pressure being equalised between the two Pre-chambers. Pre-chamber 2 (205) is located lower than Pre-chamber 1 (280), and since the pressure has been equalized, the strong liquid is allowed to run down into Pre-chamber 2 (205) under the influence of gravity. Once the liquid level is raised in Pre-chamber 2 (205), the liquid level sensor (215) sends the signal to close solenoid valve (284) and no further solution runs down from Pre-chamber 1 (280) to Pre-chamber 2 (205). A check valve (282) prevents any backward flow from Pre-chamber 2 (205) to Pre-chamber 1 (280).

Heat is applied to Pre-chamber 2 (205), resulting in a steam pressure arising from the ammonia/water solution, this causing a higher pressure in this area and driving all the liquid into the Generator (220). When the fluid level (225) in the Generator (220) rises above the fluid level sensor (230), the solenoid valve (286) is pulsed precisely through a pulse width modulation process. The pulse waveform is determined by an electronic processor (380—FIG. 3), such waveform being such as to deliver a precise quantity of weak liquid to the Absorber (265). The means by which this waveform is determined is detailed later. The amount of liquid to be delivered is determined by an electronic processor (380—FIG. 3) in response to environmental data such as required cooling power or cooling temperature, ambient temperature, machine pressures and temperatures. This allows a fine gram optimization not currently possible with other absorption chillers.

The condenser (235) condenses the ammonia gas delivered from the Generator (220), and the condensed ammonia collects to form a fluid level (240). When the fluid level (240) reaches the fluid level sensor (245), this sensor communicates this state to the electronic processor (380—FIG. 3), which subsequently controls the solenoid valve (250) to deliver a precise quantity of liquid to the evaporator The exact “dose” of liquid is determined by the processor using a software algorithm that includes data such as ambient temperature conditions, cooling power and/or cooling temperature requirements, internal pressure measurements. machine temperatures and fluid levels. The electronic Processor achieves this precise dosing through pulse width modulation of the solenoid valve (250).

The invention allows for the concentration of the ammonia/water solution to be changed during the course of the machine operation, in response to varying demands and environmental conditions. This is facilitated by a novel means of adding or removing liquid ammonia from the absorption refrigeration system via an Ammonia storage chamber, illustrated in FIG. 2. The ammonia storage chamber may be a discrete storage chamber, or the storage area may be integrated into parts of the condenser itself.

An ammonia concentration sensor may optionally be used to measure the ammonia concentration of the ammonia/water solution and make changes accordingly. Existing ammonia concentration sensors are expensive. Furthermore, the commonly available ones do not typically work well at the high concentrations of ammonia found in ammonia/water absorption machines. Consequently, whilst some embodiments may use a dedicated ammonia concentration sensor, an example embodiment of the invention provides for a means of using a pressure sensor 276 and temperature sensor 275 in combination to obtain estimates of the ammonia concentration. The pressure sensor and temperature sensor should be located in close proximity to one another in the region where the ammonia concentration is to be measured. It can be shown mathematically that for temperatures between 75 degrees centigrade and 95 degrees centigrade, and pressures between 7 and 15 bars, the concentration can be linearly approximated by the following formula:

C=(−0.00012*T+0.0245)*(P+1)−0.003015*T+0.415

-   Where: -   P is the Relative pressure in Bar. -   T is the temperature in degrees Centigrade. -   C is the ammonia concentration, being the ratio of the Mass of     ammonia in the solution to the total Mass of the solution.

In an example embodiment of the present invention, an electronic processor may take the data from a Temperature sensor (275) and a Pressure sensor (276), and compute the ammonia concentration using a formula similar to the one described previously, or other such formula as may be deemed to be accurate in estimating the ammonia concentration of the solution. Depending on user settings, ambient temperatures or other factors. the processor may adjust the concentration up or down. To increase the concentration of ammonia in the absorber (265), the processor will generate an appropriate pulse width modulated signal to solenoid (290), in order to allow a quantity of liquid ammonia from the ammonia storage chamber to move to the evaporator (255). The processor computes the correct pulse width waveform (i.e. pulse width, duty cycle and pulse frequency), by either calculating this from a formula, or looking up via the data look up table stored in its memory. The pulse width required will depend on the volume of ammonia to be dosed into the evaporator and the pressure of the liquid. The relationship between these variables for the particular solenoid used may be determined experimentally in advance and this data may be incorporated into the firmware running on the electronic processor. Either very short pulse widths, or very infrequent pulsing of solenoid valve (290) may be used to reduce the flow of ammonia liquid into the evaporator, thus causing an increase in the liquid ammonia fluid level of the ammonia storage, and resulting in a corresponding reduction in ammonia concentration in the absorber (265). The processor may optionally also apply pulses of specific types to an optional solenoid valve (288) which may be placed between the condenser and the ammonia storage, thus dosing either more or less liquid ammonia into the ammonia storage, as may be required in order to control the ammonia storage levels and corresponding ammonia concentration in the absorber (265) The correct pulse widths, duty cycles and frequencies to apply for these various operations may be computed by the processor (380—FIG. 3), using the pressure of the liquid and the amount of liquid to be passed. These operations result in a particular quantity of ammonia being stored in liquid form in the storage area, thus removing a certain amount of ammonia from the refrigeration cycle. This in turn results in a reduced concentration of the ammonia/water solution which in turn results in a lowering of the cooling temperature of the Evaporator. This mechanism may be used to optimise both cooling temperatures and cooling power of the refrigeration machine.

The present invention utilizes pulse width modulation to deliver precise quantities of liquid from one part of the machine 200 to another. The inventions Electronic control system (300) is illustrated in the block diagram of FIG. 3. Pressure sensors (305), located in various parts of the absorption refrigeration machine, provide pressure data to the Electronic processor unit (380). This pressure data is used to optimize the operation of the Generator-absorber valve (325), the Condenser-Evaporator valve (330), the Absorber-Pre-chamber Valve (320) and other valves and actuators as may be used in various embodiments of the present invention. A computer memory (315) contains data relating to the correct pulse width modulation signal required for the solenoid valve to pass a particular volume of liquid, given a particular pressure. In certain embodiments, this may be in the form of a database or “look up table”, whereby the volume of liquid passed given a particular pulse width and pressure are stored in a table. The relationship between the various variables determining the volume of fluid which is dispensed with varying solenoid coil pulse widths, voltages, duty cycles, pulse frequencies and fluid pressures are determined experimentally for each solenoid valve in advance, and this data is incorporated into the firmware running on the electronic processor. In other embodiments this may be mathematically expressed in a formula, and the software would use this formula to compute the correct waveform. The electronic processor unit, using the various data gathered from the attached temperature, pressure and machine settings, is able to determine the optimum liquid volumes to be dosed from the Condenser to the Evaporator, and from the Generator to the Absorber, and at the appropriate times (determined by the liquid level sensors), the electronic processor unit delivers the correct pulse width modulated signal to the solenoid valves to deliver this correct dosing.

FIG. 5 shows an example of a pulse width modulated signal that may be used to energise a solenoid valve. At time t1, the solenoid valve coil voltage is increased from Vclose to Vopen, and is held at this voltage for a period T1. The following pulse in FIG. 5 is of a longer duration T2, which would result in a higher volume of liquid being passed by the solenoid. In certain embodiments, a series of shorter pulses may be used to deliver the required volume of liquid, with the time spacing between pulses being varied according to the desired fluid flow. In other embodiments a longer pulse width may be used instead to achieve the same effect.

Electronic processor unit (380) may also control the ammonia/water concentration mechanism of the invention, described previously, for example through activation of solenoid valves (335) and (340). Processor 380 uses data from sensors to determine the operation of these valves, such sensors may include liquid level sensors, discrete ammonia concentration sensors, or pressure sensor and temperature sensor data, in which case the processor will compute an approximate ammonia/water concentration using a suitable mathematical formula,

Electronic processor unit (380) is also used to control the waste heat rejection, otherwise referred to as back-cooling apparatus (345). Absorption refrigeration machines are heat driven heat pumps, and as such produce much waste heat which must be rejected. It is critically important that adequate levels of back-cooling are maintained, both for efficiency of the refrigeration unit, and for the safe operation of same. In the event that back cooling is inadequate, it is important to stop the heating input to the Generator immediately. Electronic processor (380) monitors Back cooling temperature via sensors (365), and also the flow of back-cooling, liquid via flow sensors (355). In the event that inadequate flow or elevated temperature of back-cooling liquid occurs, the processor (380) will deactivate the hot water pump (350), or any other heating supply mechanism which may be supplying heating to the generator. Processor (380) also monitors the Generator temperature via temperature sensors (370), and will automatically activate back-cooling apparatus (345) whenever the temperature exceeds a threshold value. This is regardless of the user settings or operation of the machine. Furthermore, processor (380) continually monitors ambient temperatures and may activate the back-cooling apparatus (345) whenever ambient temperature exceeds a threshold value, regardless of the user settings or operational state of the machine.

Processor (380) has a communications interface (310), which provides user control and information. Such interfaces may include, but are not limited to front panel indicators and controls, web interfaces, remote control interfaces and remote data logging and supervisory controls.

FIG. 4 illustrates an alternative embodiment of the present invention. System 400 is a refrigeration machine comprising a number of interconnected fluid operating devices, with System 400 controlled by an electronic controller connected to a number of sensors and solenoid valves. The system is an absorption refrigerator, and the embodiment discussed uses ammonia as the refrigerant and water as the absorber, but any combination of refrigerant and absorber could just as well be utilized in an alternative embodiment of the present invention. The description will be limited to the example of an ammonia/water absorption cycle. Devices to determine the presence or absence of a liquid level are used in System 400, these referred hereinafter as liquid level sensors.

Generator 1 (454) contains strong refrigerant/absorber solution. For example in the case of an ammonia water absorption machine, this is an ammonia/water solution. This solution is heated and boiled in Generator 1 (454), and the resulting ammonia gas passes through to a Condenser (450), where it is condensed to liquid ammonia. The remaining ammonia/water mixture in Generator 1 (454) has a lower concentration of ammonia, since some of the ammonia has been boiled out of the solution.

Ammonia liquid which has condensed in Condenser (450) passes through to a Condenser Store (448), where it forms a liquid level (482). A convenient means of determining the liquid level is implemented in the Condenser Store (448), with the liquid level data being communicated to a central electronic controller. In one embodiment, the means of determining liquid levels may consist of a number of discrete liquid level sensors placed linearly at different heights. This arrangement is illustrated as Liquid Level sensor L9 through L13 in FIG. 4. The electronic controller sends pulse width modulation, signals to Solenoid Valve SV4 (434) in order to allow liquid ammonia in the condenser store to pass through to the Evaporator (432). Since the Evaporator is at lower pressure, the liquid ammonia passes through quickly and the process of evaporation of the liquid ammonia occurs, resulting in a cooling action. The electronic controller initiates the pulse width modulation (PWM) signals to Solenoid Valve SV4 in response to a particular liquid level being detected by the liquid level sensors. The electronic controller is user programmable and/or user selectable via a control interface, in order to determine the “set point” at which pulsing of SV4 should cease in response to the ammonia liquid level falling to a particular level in the Condenser Store (448). This allows a user configurable amount of ammonia liquid to remain in storage in the Condenser Store (448), rather than the full amount of ammonia being circulated in the refrigeration process. This results in the ammonia/water concentration being electronically variable by setting different liquid level set points for control of solenoid valve SV4 (434). The result allows for different cooling temperatures or cooling power to be determined via the electronic controller.

One or more liquid level sensors are positioned in Generator 1 (454), in order to determine the liquid level of the ammonia/water solution. This sensor arrangement is shown as L7 (452). When L7 (452) determines that there is no liquid present at liquid level (468), it activates a pulse width modulation signal to solenoid valve SV1 (456). The solenoid SV1 (456) is pulsed in order to pass the liquid through to Generator 2 (455). Here the liquid is heated and boiled again. This second generator process allows more ammonia to be boiled out of the solution, resulting in a lower ammonia/water concentration of the resulting liquid passing into Absorber 1 (430). The resulting purer water is able to more readily absorb ammonia gas in the absorption process, as compared to other existing technologies, and this has many benefits. This allows for a lower pressure in the evaporator for an equivalent back-cooling temperature, where hack-cooling is the removal of heat from the absorber, usually to the ambient temperature. Usually in order to operate in high ambient temperatures (for example desert climates), absorption chillers require high Generator heating temperatures, in order to drive out sufficient ammonia as in the Generator process to allow for sufficiently low concentrations of ammonia in the absorber. If ammonia concentrations in the Absorber are too high, then the pressures are too high and cooling at low temperatures is not possible. However if heating is to be achieved using inexpensive solar thermal hot water panels, then usually a very high heating temperature is not possible, since these types of panels typically only produce hot water at maximum temperatures of around 90-100 degrees Centigrade. In this case, existing technologies require low back-cooling temperatures to cool the absorber sufficiently to reduce the pressure to a level where cooling can occur at low enough temperatures. The ammonia/water concentrations in the absorber are simply too high. However in hot climates it is usually not possible to provide back-cooling temperatures that are low enough, because the ambient temperatures are too high, and the air conditioning cooling towers cannot provide cool enough water for back-cooling. System 400 achieves the desired low concentration of ammonia in the Absorber, despite low heating temperatures, through the process of boiling the solution a second time in Generator 2 (455). Liquid level sensor L8 (460) detects liquid level (470), thus allowing the controller to send PWM pulses to Solenoid Valve SV2 (466), thus allowing liquid to pass into Absorber 1 (430) according to the liquid level status in Generator 2 (455).

The ammonia/water solution in Absorber 1, having low concentration of ammonia, readily absorbs the ammonia gas passing into Absorber 1 (430) front the Evaporator (432). After absorbing the ammonia gas stronger ammonia/water solution passes from Absorber 1 (430) to Absorber Storage 1 (428).

The electronic controller initiates the action of the pressure Injector 1 (420 and 416), according to a detailed set of conditions being satisfied. It initiates the action of the pressure Injector 1 by opening solenoid valve SV3 (424), which allows the pressure difference between Pressure Injector 1—Feed (420) and Absorber Storage 1 (428) being equalized. Since Pressure Injector 1—Feed (420) is located at a lower position in the machine, after the pressure has been equalized, solution runs from Absorber Storage 1 (428) to Pressure Injector 1—Feed under the influence of gravity, via a one way valve (426). The electronic controller's conditions for opening and closing the solenoid valve SV3 (424) are hereinafter referred to as the “Opening conditions” and “Closing conditions” respectively. The electronic controller may include a separate timer, dedicated to controlling Pressure Injector 1. The electronic controller repeatedly looks to see if the “Opening conditions” are satisfied, and if they are that SV3 (424) is opened, initiating the cycle for the Pressure Injector 1.

In a preferred embodiment of the invention, the Opening conditions for SV3 (424) may include:

-   -   1. Greater than a specific (preset) amount of time (hereinafter         referred to as T1) has passed since the resetting of the tinier,         which occurred in Pressure Injector 1's previous cycle.         -   AND     -   2. Liquid level sensor L3 (422) of Pressure Injector 1—Feed         (420) indicates a dry condition (no liquid present), and is thus         ready to receive fluid.         -   AND     -   3. Liquid level sensor L2 (410) of Absorber Storage 2 (411)         indicates a dry condition (no liquid present), thus indicating         that the second Pressure injector is ready, and will not be         overwhelmed with fluid from the first Pressure Injector.

If all the above conditions are satisfied, then the controller opens solenoid valve SV3 and liquid flows into Pressure Injector 1—Feed (420), also referred to as “the pre-chamber”, via one way valve (426). The electronic controller may reset the timer for Pressure injector 1 at this point. Provision may optionally be made to heat the liquid slightly in Pre-chamber (420), should this be advantageous to the thermodynamics of the system.

Pressure Injector 1—Feed (420) is connected to Pressure injector 1—Boiler (416), via a syphon mechanism. Once the liquid level in the chamber (420) reaches the syphon's to point, it drains down into the boiler (416). Here it is heated, which results in a steam pressure which drives all the liquid out to Absorber 2 (412) via a one way valve (414).

The solenoid valve SV3 remains open until such time as the Closing conditions are met. The Closing conditions may include:

-   -   1. Liquid Level sensor L4 (418) of Pressure Injector 1—Boiler         (416) records a wet signal, indicating the presence of liquid         forming a liquid level (478),         -   AND     -   2. Greater than a specific, preset amount of time has passed         since the resetting of the timer, which occurred at the point of         the last opening of solenoid valve SV3, this amount of time         hereinafter referred to as T2. This is a “debounce” mechanism,         which prevents the valve being closed prematurely. In practice,         the time T2 would be much less than the total cycle time T1.

In an alternative embodiment, the Closing conditions may include an observation of a slight increase in pressure in Pressure Injector 1—Boiler (416). This increase in pressure would indicate that the steam pressure had commenced pumping the liquid into the Absorber 2 (412). Monitoring of pressure in chamber 416 would be achieved using a suitable pressure measurement device, such as an electronic pressure transducer, or other suitable pressure sensor as would be known to those skilled in the art.

Ammonia/Water solution pumped into Absorber 2 (412) via one way valve (414) has its ammonia concentration fortified through the action of the additional ammonia gas expelled from Generator 2 (455). The resultant very strong ammonia/water solution is then pumped back into Generator 1 (which operates at a higher pressure level) via Pressure Injector 2 apparatus (411, 475 and 402) and one way valve 458.

Pressure injector 2 works under very similar principles as Pressure Injector 1. The electronic controller controls Pressure Injector 2 by opening and closing Solenoid Valve SV5 (464), and does so according to precise opening and closing conditions. The electronic controller may have a dedicated timer specifically for controlling Pressure Injector 2.

In a preferred embodiment of the invention, the Opening conditions for SYS (464) may include:

-   -   1. Greater than a specific (preset) amount of time (hereinafter         referred to as T3) has passed since the resetting of the timer,         which occurred in Pressure Injector 2's previous cycle.         -   AND     -   2. Liquid level sensor L5 (406) of Pressure. Injector 2—Feed         (475) indicates a dry condition (no liquid present), and is thus         ready to receive liquid.         -   AND     -   3. Liquid level sensor L1 (410) of Absorber Storage 2 (411)         indicates a wet condition (liquid is present), thus indicating         that there is sufficient liquid available in the Absorber         Storage 2 (411) to initiate a new pressure injection cycle of         Pressure Injector 2.

If all the above conditions are satisfied, then the controller opens solenoid valve SV5 and liquid flows into Pressure Injector 2—Feed (475), also referred to as “the pre-chamber”, via a one way valve (408). The electronic controller may reset the timer for Pressure Injector 2 at this point. Provision may be made to pre-heat the liquid slightly in the Pre-chamber (475), which may assist in preventing premature boiling of the liquid before it reaches the Generator 1 (454).

Pressure Injector 2—Feed (475) is connected to Pressure Injector 2—Boiler (402), via a syphon mechanism. Once the liquid level in chamber (475) reaches the syphon's top point, it drains down into the boiler (402). Here it is heated, which results in a steam pressure which drives all the liquid Out to Generator 1 (454) via a one way valve (458).

The solenoid valve SV5 (464) remains open until such time as the closing conditions are met. The Closing conditions may include:

-   -   1. Liquid. Level sensor L6 (404) of Pressure Injector 2—Boiler         (402) records a wet signal, indicating the presence of liquid         forming a liquid level (476).         -   AND     -   2. Greater than a specific, preset amount of time has passed         since the resetting of the timer, which occurred at the point of         the last opening of solenoid valve SV5 (464), this amount of         time hereinafter referred to as T4. This is a “debounce” feature         which prevents the valve being closed prematurely. In practice,         the time T4 would be much less than the total cycle time T3.

In an alternative embodiment, the Closing conditions may include an observation of a slight increase in pressure in Pressure Injector 2—Boiler (402). This increase in pressure would indicate that the steam pressure had commenced pumping the liquid into Generator1 (454). Monitoring of pressure in chamber 402 would be achieved using a suitable pressure measurement device, such as an electronic pressure transducer, or other suitable pressure sensor as would be known to those skilled in the art.

After the strong ammonia/water solution is injected back, into Generator 1 (454) via Pressure Injector 2 (475 and 402), and one way valve (458), it is then reheated in Generator 1 (454), and the entire process repeats itself. 

1. A refrigeration machine including: fluid operating devices; and one or more pulse width modulated valves for controlling fluid flow between the fluid operating devices.
 2. The machine as claimed In claim 1, wherein the fluid operating devices include two or more of a condenser, an evaporator, a generator, an absorber, a fluid storage device, and one or more pre-chambers.
 3. The machine as claimed in claim 1, not requiring a fluid pump.
 4. The machine as claimed in claim 1, wherein one or more of the devices operate at high fluid pressure, and one or more of the devices operate at low fluid pressure.
 5. The machine as claimed in claim 1, wherein the devices include a generator, and a first pre-chamber for supplying fluid to the generator.
 6. The machine as claimed in claim 5, wherein the devices further include a second pre-chamber for supplying fluid to the first pre-chamber responsive to a deficient fluid level i the first pre-chamber.
 7. The machine as claimed in claim 5, further including a heater for heating fluid in the first pre-chamber.
 8. The machine as claimed in claim 1, wherein the devices include an absorber for receiving fluid from a generator via one of the PWM valves when a fluid level in the generator exceeds a predetermined threshold.
 9. The machine as claimed in claim 1, wherein the devices include a condenser for condensing fluid received from a generator, and for providing fluid to an evaporator via one of the PWM valves when a fluid level in the condenser exceeds a predetermined threshold.
 10. The machine as claimed in claim 1, wherein the devices include a fluid storage device to facilitate control of fluid concentration in the machine.
 11. The machine as claimed in claim 10, wherein a pulsed valve is located between the fluid storage device and an evaporator.
 12. The machine as claimed in claim 1, further including an absorber coupled to a pre-chamber via a unidirectional valve.
 13. The machine as claimed in claim 1, further including pressure and temperature sensors configured to determine fluid concentration.
 14. The machine as claimed in claim 1, wherein the fluid includes ammonia.
 15. The machine as claimed in claim 14, wherein concentration is determined using the equation: C=(−0.00012*T+0256)*(P+1)−0.003015*T+0.4515 Where: P is the Relative pressure in Bar. T is the temperature in degrees Centigrade C is the ammonia concentration, being the ratio of the mass of ammonia in the solution to the total Mass of the solution.
 16. The machine as claimed in claim 1, further including a controller configured to control the pulsed PWM valves and therefore fluid flow between the fluid operating devices.
 17. The machine as claimed in claim 1, further including a back cooling apparatus for impeding overheating of the machine.
 18. The machine as claimed in claim 1, further including a hot water system for supplying hot water to a generator.
 19. The controller for controlling a refrigeration machine, the machine including fluid operating devices and one or more pulse width modulated (PWM) valves for controlling fluid flow between the fluid operating devices, the controller configured to: control one or more pulse or PWM signals to said valves.
 20. The refrigeration method including the step of: pulse width modulating (PWM) valves to control fluid flow between fluid operating devices. 